Submerged hot gas heat exchanger

ABSTRACT

A submerged hot gas heat exchanger has a combustion gas sparge pipe with delivery ports along its upper surface, vertical fins connected to the outer peripheral surface of each heat exchanger tube, and a process liquid inlet header tank provided as a double tube structure. Baffle plates are provided in each of the tubes in a heat exchanger process liquid evaporating zone so that a heat exchanging liquid may positively rise between the tubes, heat exchange from the heat exchanging liquid to the process liquid and gas may increase, film boiling by which non uniform gasification is obtained in the tubes may be prevented and the heat exchanger may be made smaller and less expensive.

United States Patent 11 1 Ohara et al.

[ 1 SUBMERGED HOT GAS HEAT EXCHANGER [76] lnventors: Akira ()hara, 591-4 Niina, Minoo City, Osaka; Masa Takahashi, 3-418 Taito, Taito-ku, Tokyo, both of Japan 22 Filed: June 22, 1973 21 Appl. No.: 372,584

[52] US. Cl 126/360 A [51] Int. Cl. F24h 1/20 [58] Field of Search 126/360 A; 165/183, 175,

[30] Foreign Application Priority Data May 13, 1975 3,738,353 6/1973 Santoleri 126/360 A Primary Eraminer-Charles J. Myhre Assistant E.\'uminerWi1liam C. Anderson Attorney, Agent, or FirmWatson, Cole. Grindle & Watson [57] ABSTRACT A submerged hot gas heat exchanger has a combustion gas sparge pipe with delivery ports along its upper surface, vertical fins connected to the outer peripheral surface of each heat exchanger tube, and a process liquid inlet header tank provided as a double tube structure. Baffle plates are provided in each of the tubes in a heat exchanger process liquid evaporating Zone so that a heat exchanging liquid may positively rise between the tubes, heat exchange from the heat exchanging liquid to the process liquid and gas may increase, film boiling by which non uniform gasification is obtained in the tubes may be prevented and the heat exchanger may be made smaller and less expens1ve.

1 Claim, 4 Drawing Figures PATENTED HAY I 3 I975 F/G.l

FIG.2

SUBMERGED HOT GAS HEAT EXCHANGER This invention relates to a submerged hot gas heat exchanger for gasification of such a low temperature pro' cess liquid as liquefied natural gas from liquid to gas, and more particularly to a submerged combustion type vaporizer.

U.S. Pat. No. 3,368,548 discloses a submerged combustion heat exchanger. However, in such a heat exchanger, due to the arrangement wherein hot gas from the burners is discharged into the water through aperatures at the periphery of the lower terminal portion of the shroud located in the center of a tank, the heat exchanger tubes near the apertures will be in good contact with high energy bubbling heat exchanging liquid although, for the heat exchanger tubes away from the apertures, the energy of the bubbling heat exchanging liquid will reduce. The heat transmission will therefore reduce and the heat transmission of the pipes will most likely be nonuniform. Therefore, it is difficult to increase the heat exchanging capacity by increasing the rows of tubes and it is necessary to enclose the tubes with a weir so that the heat exchanging liquid heated by hot gas may rise across the tubes. Further, as the process fluid inlet header is of a single tube structure, in the event the liquid passes through the liquid inlet header, it will be heated by the high temperature heat exchanging liquid outside the header and a part of the liquid in contact with the header inner wall will be gasified to form a film layer (film boiling). This film layer of only the gas will be likely to flow into the heat exchanger tubes near the header inlet and only the liquid will flow into the tubes far from the header inlet. The flow into each tube will not only be nonuniform, but it will be difficult to obtain a uniform gasification in the heat exchanger tubes.

Furthermore, when the low temperature process liquid flowing through the tubes receives heat from the heat exchanging liquid outside the tubes and boils so as to be gasified, film boiling will occur on the inside wall of the tubes, the heat transmitting rate will reduce due to the presence of the boiling film and the heat energy of the heat exchanging liquid outside the tubes will be difficult to transmit to the low temperature process liquid in the tubes. Therefore, in order to completely gasify the low temperature liquid, it is necessary to elevate the temperature of the heat exchanging liquid. But, if the liquid temperature is high, the heat losses by the vaporization of the heat exchanging liquid, the heat radiation from the outside wall of the heat exchanging liquid containing tank and the heat energy of the waste gas discharged through the heat exchanging liquid will be large. Therefore, such as apparatus must be large with the consequent maintenance costs being high.

An object of the present invention is to provide a submerged hot gas heat exchanger wherein no weir is required and the thermal efficiency is high.

Another object of the present invention is to provide a submerged hot gas heat exchanger wherein the process liquid inlet header tank is provided as a double structure to prevent nonuniform gasification.

A further object of the present invention is to provide a submerged hot gas heat exchanger wherein a spiral baffle plate of a simple structure is provided in the process liquid evaporating zone within heat exchanger tubes to prevent unfavorable film boiling.

In the drawings:

FIG. 1 is a partly sectioned view of a submerged hot gas heat exchanger embodying the present invention;

FIG. 2 is a sectional view taken along line II II of FIG. 1;

FIG. 3 is a sectional view of an inlet header tank part having a double structure to prevent nonuniform gasification; and

FIG. 4 is a partly sectional elevational view of a finned heat exchanger tube of another embodiment for preventing film boiling as in the manner of FIG. 3.

In FIGS. 1 to 3, a tank 1 provided for containing a heat exchanging liquid, is sealed at its upper portion with a lid plate 17 and is fitted at its center with an exhaust stack 18. A burner 2 is mounted at the upper end of tank 1 and has a high temperature combustion gas jetting port directed downwardly. A combustion gas cylinder 3 directs a combustion gas downwardly into the liquid, and is connected at its upper end with burner 2. Cylinder 3 has a combustion gas sparge pipe connecting flange 7 at the side near its lower end. A combustion gas sparge pipe 4 is horizontally disposed and is connected at one end to combustion gas cylinder flange 7. Pipe 4 has a plurality of through apertures 8 located along its upper surface for the jetting of combustion gas into the liquid. Heat exchanger tube sections 5 of an elongated tube are disposed in parallel relation and are bent at their opposite ends to form such an arrangement as shown in FIG. 1. Upper and lower vertical fins 19 are provided along each pipe section, and opposite ends of the tube are welded to header tanks 10 and 11 so that the processed liquid may pass therethrough. A heat exchanging portion.6 is formed of a plurality of tubes 5, as well as of liquid inlet header tank 10 and gas outlet header tank 11. A small diameter tube 12 is provided with a plurality of process liquid delivering orifices 9 along its lower surface in a lengthwise direction, and is located in liquid inlet header tank 10 so as to render the inlet header tank a double tube structure. 13 and 14 are inlet and outlet flanges, respectively. 15 is process liquid inlet tube. 16 is a gas outlet tube.

Another embodiment designed for preventing the formation of film is shown in FIG. 4. Here, a spiral baffle plate 20 having an outer diameter smaller than the inner diameter of tube 5 is disposed in the tube sections in the evaporating zone.

The apparatus according to the present invention is comprised of the structure as described above.

A combustion gas generated in burner 2 will pass through combustion gas cylinder 3 and combustion gas sparge pipe 4, and will be jetted through aperture 8 at a high speed into the liquid. The combustion gas and heat exchanging liquid will exchange the heat energy while mixing together, and will at the same time violently flow upwardly as in the manner of an air lift. It will quickly pass through between the tube sections, and will at the same time transmit the heat energy of the liquid to the process low temperature liquid flowing through tubes 5. It will overflow out of heat exchanging part 6, will flow downwardly, will be again heated by the combustion gas below the heat exchanging portion and will circulate within the tank.

It should be noted that the combustion gas will separate from the liquid in the upper portion of the tank and will be discharged through exhaust stack 18.

On the other hand, the process liquid to be gasified from a liquid to a gas will flow into inlet header tank 10 through inlet flange l3 and inlet tube 15, will flow out through delivering orifices 9 of small diameter tube 12 and will flow into the respective heat exchanging tube sections through the annular passage formed between the inner wall of the inlet header tank and the outer wall of the small diameter tube. The process liquid in the tube will absorb evaporating heat from the bubbling heat exchanging liquid outside the tubes while moving from the lower end of the tube, will be gradually gasified, will become a complete gas at the upper end of the tube and will be emitted out through outlet header tank 11, gas outlet tube 16 and outlet flange M.

In this embodiment, as mentioned above, since the inlet header tank is of a double structure, no nonuniform gasification is possible and, when the process liquid flows into tubes 5, a film boiling will be generated on the inner wall of tubes 5, although the process liquid will be given a torque by spiral baffle plate 20 provided in the evaporating zone and will be splashed by its centrifugal force so as to break the gas film.

Thus, the film boiling on the inner wall of the tubes will be avoided the efficiency of heat transmission from the heat exchanging liquid to the process liquid in the tubes will improve, and the process liquid will become a complete gas at the upper end of the tubes and will be emitted through outlet header tank 1], outlet tube 16 and outlet flange 14.

In the present invention, as mentioned above, as the combustion gas is jetted into the liquid through the upper surface of the combustion gas sparge pipe located in the center below heat exchanging portion 6, irrespective of the particular arrangement of each tube section 5, heat will be transmitted substantially uniformly and a perfect gasification of the liquid in each of the tube sections will result. Also, since a pair of fins are provided on the outer peripheral surface of the tube sections, the heat transmitting area of the tubes will be enlarged, heat transmission through the tubes will increase and at the same time the fins will form a flowing passage for the combustion gas and heat exchanging liquid between the respective tube sections so that the bubbling heat exchanging liquid may positively rise through therebetween. Therefore, a weir for enclosing the tubes heretofore required will not be necessary. Further, as the process liquid inlet header tank is a double tube structure, a uniform gas-liquid mixed condition of the gas portion and liquid portion will be obtained before they flow into each tube so that a uniform favorable gasification is possible.

An experimental example to confirm the effect of the embodiment of FIG. 4 wherein a spiral baffle plate is located within the tubes will now be shown.

In order to gasify 15 tons of a liquefied natural gas per hour, with the conventional heat exchanger, the temperature of the heat exchanging liquid was required to be 64C. and the thermal efficienty was only However, using the heat exchanger of the invention wherein baffle plates are inserted in the tubes, the required liquid temperature was 26C. and the thermal efficiency reached was 99%. That is to say, with this embodiment, the liquid temperature could be reduced by about 40C. and the efficiency could be elevated by 20%.

In this embodiment, as mentioned above, by merely adding a simple structure wherein spiral baffle plates are inserted into the evaporating zone within the tubes, the growth of film boiling by the gasification of the process liquid in the tube can be prevented, the condition of a nucleate boiling can be always maintained and the heat losses can be reduced, and the apparatus can be inexpensively constructed.

What is claimed is:

l. A submerged hot gas heat exchanger, comprising, a tank containing a heat exchanging liquid, a burner mounted at the upper end of said tank, a combustion gas shroud connected with said burner and extending into the lower portion of said tank, a combustion gas sparge pipe connected with said shroud at its lower end, said sparge pipe having a plurality of apertures along its upper surface for jetting air and combustion gases into the liquid, a tube located within said tank above said sparge pipe, said tube being bent into a plurality of parallel tube sections for the passing of a process liquid therethrough, upper and lower vertical fins attached to said tube sections, inlet and outlet header tanks connected to opposite ends of said tube, said tanks along with a part of said tubes forming a heat exchanging portion and means for preventing film boiling being provided in the said heat exchanging portion, wherein said means includes a small diameter tube located within said inlet header tank, said tube having a plurality of orifices along its lower surface for delivering a liquid to be treated. 

1. A submerged hot gas heat exchanger, comprising, a tank containing a heat exchanging liquid, a burner mounted at the upper end of said tank, a combustion gas shroud connected with said burner and extending into the lower portion of said tank, a combustion gas sparge pipe connected with said shroud at its lower end, said sparge pipe having a plurality of apertures along its upper surface for jetting air and combustion gases into the liquid, a tube located within said tank above said sparge pipe, said tube being bent into a plurality of parallel tube sections for the passing of a process liquid therethrough, upper and lower vertical fins attached to said tube sections, inlet and outlet header tanks connected to opposite ends of said tube, said tanks along with a part of said tubes forming a heat exchanging portion and means for preventing film boiling being provided in the said heat exchanging portion, wherein said means includes a small diameter tube located within said inlet header tank, said tube having a plurality of orifices along its lower surface for delivering a liquid to be treated. 